Silane is important in the production of electronic equipment and devices. It is an intermediate used to prepare polysilicon, which is used to prepare monocrystalline silicon for use in semiconductor devices.
Amine alanes, complexes of tertiary amines with AlH.sub.3, are used in various reduction processes, in the preparation of aluminum, and also in the production of silane.
The production of amine alanes has been accomplished by several methods. These are discussed in Marlett, et al., U.S. Pat. No. 4,757,154 (issued July 12, 1988) and in references cited therein, and in Marlett, U.S. Pat. No. 4,474,743 (issued Oct. 2, 1984) and in references cited therein.
The reaction of tetrachlorosilane (silicon tetrachloride) with alkali metal aluminum hydride and tertiary amine to produce silane and amine alane is disclosed in Marlett, U.S. Pat. No. 4,757,154.
The behavior of trichlorosilane with tertiary amines has been addressed by several references. Burg, "Trimethylamine Adducts of the Chlorosilanes," J. Am. Chem. Soc., 1954, 76, 2674-2675, gives evidence for adduct formation between all mixed chlorosilanes and trimethylamine. There was no evidence for a trimethylamine adduct with SiH.sub.4, and the adduct with SiCl.sub.4 decomposed above -54.degree. C. Burg also refers to the catalytic effect of trimethylamine on the disproportionation of trichlorosilane.
Ring, et al., "A New 1:1 Adduct of Trimethylamine and Trichlorosilane, Trimethylammonium Trichlorosilyl," J. Am. Chem. Soc., 1971, 93, 265-267, confirm Burg's observations on the trimethylamine-trichlorosilane adduct and present evidence of a new compound, which they characterize as the trimethylammonium salt of the trichlorosilyl anion. Decomposition of their compound with HCl in propyl ether produced H.sub.2 SiCl.sub.2 and SiCl.sub.4 as well as HSiCl.sub.3.
Benkeser, "The Chemistry of Trichlorosilane-Tertiary Amine Combinations," Acc. Chem. Res., 1971, 4, 94-100, cites a number of different reports from the literature describing amine complexes with silicon compounds of the general formula SiH.sub.4-n X.sub.n. He discusses a variety of different experimental evidence for the existence of the trichlorosilyl anion when trichlorosilane is in the presence of various tertiary amines. In this connection, Benkeser also cites Bernstein, "On the Mechanism of Interaction between Tertiary Amines and Trichlorosilane," J. Am. Chem. Soc. 1970, 92, 699-700, and Benkeser et al., "Evidence for the Existence of the Trichlorosilyl Anion," J. Am. Chem. Soc. 1970, 92, 697-698, which discuss trichlorosilane in the presence of tri-n-butylamine and tri-n-propylamine, respectively, forming tri-n-butylammonium trichlorosilyl and tri-n-propylammonium trichlorosilyl, respectively. A number of reactions of SiCVl.sub.3.sup.- can be explained as nucleophilic displacements by SiCl.sub.3.sup.- (p. 97, column 1, near bottom of page, and elsewhere in the reference).
In spite of the apparent stability of the trichlorosilyl anion in combination with tertiary ammonium cation and its penchant for reacting as a unit, it has now been discovered that the reaction of tertiary ammonium trichlorosilyl, i.e., the charge-separated complex between trichlorosilane and a tertiary amine, with alkali metal aluminum tetrahydride in the presence of additional tertiary amine to produce silane and amine alane can be made to occur. Surprisingly, this process is capable of good yields even though the complex has very poor solubility in some solvents used as liquid reaction media.